Genius

I don't want to nitpick, but it seems that when you add a new iOS 9 device to your iCloud ecosystem, the four built-in bookmarks (Apple, Bing, Google, and Yahoo) on the device's Safari browser get dumped into your ecosystem and are subsequently propagated to any and all OS X machines in that ecosystem.

Since I provided my iCloud credentials to the new device joining my ecosystem (in this case, my new iPhone 6s Plus), the ideal way to synchronize my existing Safari bookmarks with those on the new device would have been to ask me if I wanted to (a) merge bookmarks on both devices or (b) have existing bookmarks in one device overwrite those in the other. I was never given a choice; instead, Apple assumed I wanted to merge the four bookmarks mentioned above with the ones in my ecosystem.

I ented up with the four unwanted bookmarks I mentioned in my first paragraph joining my ecosystem.